Have a look at the garage door gasket material that makes contact with the ground. It's very soft and will form to uneven surfaces. Put that on the skirt Alex mentions to get a close seal. Might not be air tight but should close things off well.

Very interested in this topic myself, I am about to convert an old 10 x 12 metal shed into an obs myself. Need to replace the roof panels and strengthen the walls with interior wood framing first. Considering making the observing floor 10 x 8 and having a 10 x 4 warm room. But may not do the warm room for now...I can easily add the interior wall to do that later if wanted. Have not made up my mind yet about this mod....

I was planning on using another piece of metal to slip up under the edge of the roof panels and over the sides to overlap and cover the wood and a couple of inches of the walls but only because I already have the metal to do so...I thought about adding a rubber skirt between the wood and the overlap metal but don't know if I really need that.

Could you post some more pics of your observatory - inside and out. I would like to see how you put it all together. Hope to start mine very shortly - within the next couple of weeks preferably.

Was going to build a new one in the backyard but will build that one instead at a bortle 2 darksite property we just bought.
(2 observatories for the price of one...SCORE!!!)

Very interested in this topic myself, I am about to convert an old 10 x 12 metal shed into an obs myself. Need to replace the roof panels and strengthen the walls with interior wood framing first. Considering making the observing floor 10 x 8 and having a 10 x 4 warm room. But may not do the warm room for now...I can easily add the interior wall to do that later if wanted. Have not made up my mind yet about this mod....

I was planning on using another piece of metal to slip up under the edge of the roof panels and over the sides to overlap and cover the wood and a couple of inches of the walls but only because I already have the metal to do so...I thought about adding a rubber skirt between the wood and the overlap metal but don't know if I really need that.

Could you post some more pics of your observatory - inside and out. I would like to see how you put it all together. Hope to start mine very shortly - within the next couple of weeks preferably.

Was going to build a new one in the backyard but will build that one instead at a bortle 2 darksite property we just bought.
(2 observatories for the price of one...SCORE!!!)

Have a look at the garage door gasket material that makes contact with the ground.

That's what I used on my ROR. However, judging from the photo, if there isn't some overhang on the outside, attaching something like this may allow the rain, etc., to trickle in. You can't tell in this photo, but the black strip actually is under the wood of the roof that moves. It's flexible & allows the roof to glide right along the strip.

You know, I cannot tell how far the aluminum roofing hangs over the edge. If it is more than an inch or so, it seems a bit of flashing nailed onto that reddish lumber, just an inch or three longer than the reddish lumber is wide should do the trick. As necessary, space the bottom of the flashing (with a strip of furring or something if necessary) so it rides outside the lower wall. That really should do it.

Very interested in this topic myself, I am about to convert an old 10 x 12 metal shed into an obs myself. Need to replace the roof panels and strengthen the walls with interior wood framing first. Considering making the observing floor 10 x 8 and having a 10 x 4 warm room. But may not do the warm room for now...I can easily add the interior wall to do that later if wanted. Have not made up my mind yet about this mod....

I was planning on using another piece of metal to slip up under the edge of the roof panels and over the sides to overlap and cover the wood and a couple of inches of the walls but only because I already have the metal to do so...I thought about adding a rubber skirt between the wood and the overlap metal but don't know if I really need that.

Could you post some more pics of your observatory - inside and out. I would like to see how you put it all together. Hope to start mine very shortly - within the next couple of weeks preferably.

Was going to build a new one in the backyard but will build that one instead at a bortle 2 darksite property we just bought.
(2 observatories for the price of one...SCORE!!!)